1. Field Of The Invention
The present invention relates to a battery casing for receiving battery modules for an electric vehicle.
2. Description Of The Related Art
A battery unit used for an electric vehicle typically includes multiple battery modules and a battery casing that receives the battery modules. One type of structure of a battery casing includes a tray member that supports battery modules and a cover member that covers the top of the tray member, as disclosed in Japanese Laid-open Patent Publication No. 2010-153130 (JP 2010-153130 A). In this structure, the tray member and the cover member are coupled together by means of multiple bolts and nuts at the joint part between the periphery of the tray member and the periphery of the cover member.
The tray member included in the battery casing disclosed in JP 2010-153130 A is provided with partitioning walls extending in the width direction for dividing the tray member in the longitudinal direction, and separation walls (ribs) extending in the front-rear direction for dividing the tray member into multiple compartments. The multiple battery modules are placed into the respective sections separated by the partitioning walls and the separation walls and are secured therein.
For a larger battery casing that receives larger-capacity battery modules, a higher stiffness is required so as to withstand the weight of the battery modules. As disclosed in JP 2010-153130 A, such a battery casing is made from a fiber reinforced plastic (FRP) having the electric insulation property, and separation walls are provided to the tray member that supports the battery modules, for securing the battery modules, as well as enhancing the stiffness of the casing.
For a tray member made from a fiber reinforced plastic, in order for the separation walls provided in the tray member to secure sufficient stiffness required for the battery casing, the separation walls must be formed thicker. However, forming thicker separation walls means reduced space for receiving the battery modules on the tray member.